“Remember man, thou art dust and unto dust thou shalt return,” is part of an old prayer. I sit in the Mojave Desert in southern California as I write. The stripped-bare bones of a deer are laid out on the desert floor nearby. The bones returning to the Earth bring mortality to mind. Are we made from dust?

In a way we are, but it is a way much more interesting than dusty old theologians ever imagined. This is the story: we are all made from stars. We are, if you will, stardust.

Cosmologists only figured this out in recent decades, and it has not yet been understood widely. We are all made from stars. What could this mean?

It works like this: early in the Universe, there was a time before matter. Out of the primordial particles, hydrogen was born. It is the simplest and lightest form of matter, so it sits in the lowest box in the periodic table of the elements.

Hydrogen emerged throughout the universe. It collected in clouds as the atoms were drawn together by gravity. Eventually the clouds that formed were enormous. They became denser and denser through the mutual attraction of gravity until a crucial threshold was reached and magic happened: a ball of gas became so dense it ignited a nuclear reaction.

A star was born. Or rather untold billions of them, for it was happening throughout the Universe. This first generation of stars made of hydrogen burned and filled the Universe with light for the first time.

A star is a violent thing in delicate equipoise. It is a raging nuclear reaction that balances itself for billions of years. The nuclear fire pushes outward and this force precisely cancels the gravitational pull that would otherwise make the star collapse.

What happens in the stars’ nuclear fire is alchemy. Human alchemists claimed to make gold from base metals. In reality, every speck of gold in the Universe was made by stars. The star is a fusion furnace, where new elements are made from the simplest building block—hydrogen. Under heat and pressure a particle is added to hydrogen's core and the next simplest element—helium—is born.

Then the star begins to work on helium. A medium sized star like the Sun doesn’t get much beyond this. But in bigger stars, where the gravity is stronger and the temperature reaches a billion degrees, the process continues. Keep adding another particle to the core, and you get the next elements, through oxygen, sodium, silicon, and so on. In this way the star works its way up through the elements.

The star makes all the elements out of virtually nothing. Remember the periodic table, in which the elements are arranged from the lightest to the heaviest, the simplest to the most complex. It all depends on how many particles are added to the core. If hydrogen is the simplest, the heaviest and densest naturally occurring is uranium. That’s why spent uranium from reactors is used in armor piercing shells.

As the star ages, it makes each more complex and heavy element in its fusion core. But the heaviest elements are hard even for a star to concoct. When the star makes iron, it hits a wall. Iron is heavy. When the star has made a lot of it, the delicate balance the star has maintained gets broken. Fusion pressure no longer pushes out hard enough to balance the heavy gravitational pull of the iron. The body of the star starts falling inward.

The star implodes. Then it explodes in a supernova—an uncontrolled nuclear fire. In the heat of this fire the alchemy continues—the star makes silver, gold, platinum, and all the other heavy elements all the way up through uranium.

Exploding, the star seeds these elements into space. Some of the elements are picked up in second-generation stars. These will live for a shorter time since they start by bearing heavy elements within them. Some of the elements the star spews out will collect into planets, which is where we eventually come in.

All the matter on Earth is star stuff. The carbon in our bodies, the iron in our blood, every bit of this fleshy human thing we are was made in stars. So too every bit of the rental car I drove into the desert. So too the oxygen we breathe, and every fish in the sea. The stars made us possible through their rich and fertile exploding deaths.

So we are made of stardust, not some ordinary dust. When we look up and see the stars, we now know that their ancestors are ours as well. And we know that today's stars are still making the stuff of life in their fiery hearts all throughout the Universe.